Aerosol fractionator for large-scale sampling

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Abstract
The design of a versatile instrument for aerosol assessment is described. The single stage device incorporates the principal of virtual impaction and a continuously variable slit width to provide for ease of calibration, low internal wall losses, and potential for large‐scale sampling, as well as the option of either fractionating particles into two size classes for mass or chemical analysis or determining entire particle size distributions. Initial tests indicate the efficiency curve of the device is solely a function of particle Stokes number ψ for typical geometries and flowrates and is characterized by the cutoff value ψ1/250=0.36 ±0.04 and a steepness of ψ1/284/ψ1/250 =1.32±0.06. Moreover, wall losses are shown to peak at less than 15% at the critical Stokes number ψ1/250, which is an improvement over existing devices now used for large‐scale sampling.